As a blow molding apparatus that blow molds a resin-made preform into a container, Patent Literature 1, for example, describes a blow molding apparatus including a mold used for blow molding (hereinafter, called a blow mold), a stretching rod configured to stretch the preform, and a support pin configured to support the bottom of the preform from the outer side of the preform. The described blow molding apparatus is configured to stretch the preform in the axial direction by the stretching rod inserted into the preform and to supply pressurized air into the preform to stretch (expand) the preform in the radial direction while supporting the bottom of the preform by the support pin.
Other than the method of stretching the preform by supplying pressurized air into the preform as in the blow molding apparatus described in Patent Literature 1, the preform may be blow molded into a container by other existing methods, such as stretching the preform by supplying liquid into the preform (this method being called liquid blow molding). When such liquid blow molding is adopted to mold a container, there is the problem that the direction in which the preform is stretched and deformed is likely to be unstable due to behavior (e.g., the direction and strength of flow) of the liquid in the preform that has been supplied into the preform. For the above reason, it is needed especially in the liquid blow molding apparatus to increase stability during stretching and deformation by such a structure as the support pin described in Patent Literature 1.